gh-145546: unittest.util: fix sorted_list_difference tail deduplication#145547
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stefanzetzsche wants to merge 8 commits intopython:mainfrom
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gh-145546: unittest.util: fix sorted_list_difference tail deduplication#145547stefanzetzsche wants to merge 8 commits intopython:mainfrom
sorted_list_difference tail deduplication#145547stefanzetzsche wants to merge 8 commits intopython:mainfrom
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sorted_list_difference failed to deduplicate remaining elements when one list was exhausted, causing duplicate values in the result. Fix uses dict.fromkeys() to deduplicate before extending. sim: https://taskei.amazon.dev/tasks/TODO
…ication Exercise the except-IndexError path where one list is exhausted and the remaining tail of the other list contains duplicates. These cases were previously untested and would have passed even without the fix in the preceding commit.
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aisk
reviewed
Mar 5, 2026
aisk
reviewed
Mar 5, 2026
Misc/NEWS.d/next/Library/2026-03-05-14-13-10.gh-issue-145546.3tnlxx.rst
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dict.fromkeys requires hashable elements, which narrows the input contract. Replace with a simple consecutive-duplicate removal that only uses equality comparison, matching the main loop's approach. Add test cases for strings and unhashable types (lists).
aisk
approved these changes
Mar 5, 2026
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Problem
sorted_list_differencedoesn't deduplicate remaining elements when one list is exhausted. Theexcept IndexErrorfallback usesextend(expected[i:])/extend(actual[j:])which includes duplicates.Reproducer
Fix
Replace the raw extend(expected[i:]) / extend(actual[j:]) in the except IndexError fallback with a helper that removes consecutive duplicates. The helper only uses equality comparison (not hashing), matching the main loop's approach and preserving support for unhashable types like lists.
Tests